Always have x number of goroutines running at any time

Question

I see lots of tutorials and examples on how to make Go wait for x number of goroutines to finish, but what I\'m trying to do is have ensure there are always x number running

Answer 1

You may find Go Concurrency Patterns article interesting, especially Bounded parallelism section, it explains the exact pattern you need.

You can use channel of empty structs as a limiting guard to control number of concurrent worker goroutines:

package main

import "fmt"

func main() {
    maxGoroutines := 10
    guard := make(chan struct{}, maxGoroutines)

    for i := 0; i < 30; i++ {
        guard <- struct{}{} // would block if guard channel is already filled
        go func(n int) {
            worker(n)
            <-guard
        }(i)
    }
}

func worker(i int) { fmt.Println("doing work on", i) }